1. Field of the Invention
The present invention relates to a movable range adjusting mechanism for a workpiece conveying device.
2. Technical Field of the Invention
In a manufacturing process of a semiconductor device, a device which conveys workpieces such as semiconductor wafers is commonly used (e.g., Japanese Patent Laid-Open No. 2006-272526 and Japanese Patent Laid-Open No. 2001-300879). For example, there is a workpiece conveying device which holds a semiconductor wafer by a pair of arms driven to open and close by an actuator equipped with a cylinder, and moves the semiconductor wafer to a desired position (e.g., Japanese Patent Laid-Open No. 2003-309089). In the manufacturing of a semiconductor device, it may be necessary to convey semiconductor wafers of different sizes in some cases.
Since a conveying mechanism for semiconductor wafers is designed and adjusted according to the size of the wafer to be processed, wafers of different sizes may not be properly conveyed. For example, when the size of the semiconductor wafer is smaller than the size to which the conveying mechanism is adjusted, the holding force becomes smaller and clearance becomes too large at positions where the wafer is held, which may lead to deterioration of positioning accuracy of the wafer. On the other hand, when the size of the semiconductor wafer is larger than the size to which the conveying mechanism is adjusted, the holding force becomes too large, which may cause excessive stress on the wafer or prevent the wafer from being properly held.
In some holding mechanisms such as the arm of the conveying mechanism, a motion range thereof may be changed according to the size of the workpiece, such as the semiconductor wafer, to be conveyed. When controlling the motion range of the holding mechanism of the conveying mechanism by a motor-based actuator, the motion range can be changed by changing motion parameters of the motor (e.g., a pulse number, etc. in the case of a pulse motor). However, such a motor-based actuator tends to be costly. Motion mechanisms using a pneumatic or hydraulic actuator such as a cylinder mechanism are generally less costly than a motor-based actuator. When changing the motion range of such a cylinder-based actuator, the motion range is changed by adjusting a position of a stopper which defines the motion range. For example, the position of the stopper can be adjusted by a screw. However, when adjusting the stopper position by the screw, the stopper position may be slightly different after each adjustment operation, and repeatability and accuracy of the positioning may not be adequate. In addition, it tends to take time to adjust the stopper position when the screw is used to adjust the stopper position.